1. Field of the Invention
The present invention relates to an exposure apparatus, a surface position adjustment unit, a mask, and a device manufacturing method. More particularly, the present invention relates to an exposure apparatus used in a lithographic process to manufacture an electronic device such as a semiconductor device or a liquid crystal display device, a surface position adjustment unit suitable for adjusting the surface position of a substrate in said exposure apparatus, a mask that can be suitably used in said exposure apparatus, and a device manufacturing method using the exposure apparatus.
2. Description of the Related Art
Conventionally, in a lithographic process to manufacture a device such as a semiconductor device or a liquid crystal display device, the static type projection exposure apparatus based on the step-and-repeat method (the so-called stepper), the scanning type projection exposure apparatus based on the step-and-scan method (scanning step type projection exposure apparatus: the so-called scanning stepper), and the like have been mainly used as the projection exposure apparatus.
The semiconductor device is formed by overlaying several tens of circuit patterns onto a substrate such as a wafer; however, the line width of each pattern in each layer is not the same. That is, layers exist, such as: a critical layer which is mostly made up of a circuit pattern having a fine line width the same level as the limit of resolution of the latest edge projection exposure apparatus such as the scanning stepper using the KrF excimer laser as a light source (hereinafter summing it to “KrF scanner unit” as appropriate), a non-critical layer (also referred to as a rough layer) made up of a circuit pattern having a wider line width compared to the critical layer, and a middle layer made up of a circuit pattern which line width is in between the critical layer and non-critical layer.
In general, resolution becomes higher when the exposure wavelength is shorter, and when the exposure wavelength is the same, resolution, in other words, the minimum line width resolvable becomes finer when the numerical aperture (N.A.) of the projection optical system increases. In addition, the resolution of the static type exposure apparatus (also referred to as a one shot exposure apparatus) such as the stepper is far inferior compared with the scanning stepper, whereas, the throughput tends to be high. Accordingly, in the actual manufacturing site of a semiconductor device and the like, various types of exposure apparatus are used depending on the layer, and the same electronic device is usually manufactured using a plurality of types of exposure apparatus. As a method of using a plurality of types of exposure apparatus depending on layers, a mix-and-match; combining a scanning stepper having a short exposure wavelength (for example, a KrF scanner unit) and a stepper having a long exposure wavelength (for example, an i-line stepper), is frequently used.
In addition, with the projection exposure apparatus, it is necessary to transfer the pattern of the mask onto the substrate in a state where the surface of the substrate such as the wafer coincides with the best image-forming plane of the projection optical system. For this reason, in the projection exposure apparatus, a system to detect the position of the wafer surface in the optical axis direction of the projection optical system (hereinafter appropriately referred to as “height position”)—a height position detection system—is provided. In recent years, since the height position cannot be detected accurately when the height position measurement of the wafer is performed at only one point due to the influence of steps on the wafer surface, a height position detection system that detects the height position at a plurality of points on the wafer (hereinafter also referred to as a “multiple point AF system”) has been proposed. This multiple point AF system, for example, irradiates light having passed through a plurality of slits arranged in a predetermined pitch onto the wafer from an oblique direction, and based on the positional relationship between the light reflected off the wafer and a plurality of photo-detectors (photodetection elements) corresponding to the respective slit lights, the height position is detected with high precision at a plurality of points on the wafer.
In addition, with the height position detection system, detection of the height position becomes difficult when the height position of the wafer deviates from the best focal position and the light reflected off the wafer does not reach the photodetection area of the photodetection elements (when the height position of the wafer is off the range of the height position range detectable by the photodetection element). Also, with the multiple point AF system that irradiates a plurality of slit lights onto the wafer from an oblique direction, forms a plurality of slit images arranged in a predetermined pitch on a wafer, and individually detects the catoptric light of each slit light with a plurality of photo-detectors, if the height position of the wafer deviates from the target position, then the slit images on the wafer deviates in the arrangement direction of the slit images. When the deviation amount of the slit image on the wafer reaches half (½) the pitch of the slit image (the interval between two adjacent slit images), these catoptric lights shift one by one with respect to their corresponding photo-detectors and are incident on the photo-detectors arranged next to the corresponding photo-detectors. Accordingly, the photo-detectors excluding the ones arranged on the edge output the same signals as when the wafer surface is located at the target position. In this case, the multiple point AF system may make an error in detection and consider that the position of wafer surface is at the target position, in spite of the fact that the wafer surface is off the target position.
So, with the current projection exposure apparatus, a photoelectric sensor called a tracking sensor is arranged in general. The tracking sensor detects the deviation direction of the substrate surface from the target position, even in the case the height position cannot be detected because the height position of the substrate surface has deviated from the target position, and when the plurality of light rays for height position detection reflected off the substrate shift one by one with respect to their corresponding photo-detectors and are incident on the photo-detectors arranged next to the corresponding photo-detectors, the tracking sensor detects that the height position of the substrate is off the target position. The multiple point AF system that includes the tracking sensor is disclosed in, for example, Japanese Patent Laid Open (Unexamined) No. 07-130635, and the corresponding U.S. Pat. No. 5,569,930.
In addition, in the case of the projection exposure apparatus such as the conventional steppers, conditions contributing to improvement in throughput that has nothing to do with the improvement of resolution, such as, the stepping velocity of the substrate stage in between shots, permissible positional error on position setting settlement, and the like were always the same when exposure was performed. That is, in what is called the process program file, which is a type of database for setting exposure conditions, various control parameters were set without any options. In other words, with the conventional projection exposure apparatus the control parameters such as the stage parameter were set with the exposable minimum line width as the target; regardless of the pattern line width required.
Now, the size of the exposable maximum area (hereinafter referred to as “exposure range”) with a conventional stepper is, for example, a 22 mm×22 mm sized square, whereas with the scanning stepper the size of the exposure range is, for example, a 25 mm×33 mm sized rectangle, being different in size and shape. Therefore, when a shot area of the stepper and a shot area of the scanning stepper were overlaid based on the mix-and-match referred to earlier, and a so-called 1 in 1 exposure was performed, the actual exposure area of the scanning stepper capable of exposing a large area had to be limited to the exposure range of the stepper. Thus, the capability of the scanning stepper (large exposable range) could not be efficiently used.
On the other hand, when one shot area of the scanning stepper and two adjacent shot areas of the stepper are overlaid, and a so-called 2 in 1 exposure is performed, errors of shot rotation, shot magnification, and the like may remain since the center of the two shot areas differ.
In addition, with the conventional stepper and the scanning stepper, in accordance with the different alignment method of the masks, masks that have alignment marks with a different arrangement and number were respectively used. The mix-and-match using both the stepper and the scanning stepper that have a different exposure range size is disclosed in, for example, U.S. Pat. No. 5,989,761.
Also, with the conventional projection exposure apparatus, the measurement point corresponding to the tracking sensor was located at one or two points around the center portion within the projection area. Or, a pair of points was arranged outside a set of opposing sides of a rectangular area serving as the projection area, in the vicinity of the center portion of the remaining opposite sides. Therefore, depending on how the shot area where exposure is performed first (first shot) is set, the situation may occur when the measurement point of the tracking sensor is off the wafer upon first exposure. That is, usually for the first shot, a circumferential shot on the wafer is selected, however, in the case the circumferential shot is a so-called chipped shot, none of the measurement points of the tracking sensor will not be located on the wafer. The tracking sensor is used mainly for setting the wafer surface swiftly in the vicinity of the best focal position upon exposure of the first shot. Accordingly, in order to effectively exhibit the function of the tracking sensor, the first shot needed to be set so that the situation stated above did not occur. Thus, the arrangement of the shot area and the decision (selection) of the first shot were limited.
In addition, as is described above, with the conventional projection exposure apparatus, the parameter of the apparatus was always fixed regardless of the minimum line width subject to exposure, so exposure was performed with the same accuracy in both cases when a pattern with a fine line width was transferred and when a pattern with a wide line with was transferred. That is, even when a rough layer—subject to a pattern having a wide line width—was exposed, the same control parameters such as the permissible value of stage vibration on exposure, the positional deviation permissible value of the substrate surface with respect to the target surface on automatic focusing, and the like were set as when a middle layer or a critical layer—subject to a pattern having an arrower line width (the resolvable minimum line width set in accordance with the exposure wavelength and the numerical aperture of the projection optical system)—was exposed.
As a consequence, even in the case when the required exposure accuracy was low and more priority could have been put on throughput, exposure was performed using the same control values as of the case when the required exposure accuracy was high and priority was required on resolution.